Another "interesting" corner case:
In some cases, a minus sign is part of an <ident> token. But once
tokenization is done, we don’t know anymore if that character was
escaped in the CSS source. This is a similar issue to that of the syntax
of ID selectors.
So, what exactly do we want to allow to be escaped or not? Selectors 3
uses {N} and ['-'|'+'], which means that n can be escaped but not a plus
or minus sign.
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Simon Sapin